90 Forty-first Axxual Report on the 



some degree from the decay which takes place around the spikes and 

 under the rails, from the fact that the iron in contact with this 

 wood neutralizes its natural antiseptic. The ends and centers of 

 chestnut ties are sound after the rails have cut into the wood enough 

 to necessitate their removal. The opinion is quite prevalent that they 

 do not decay, but are mostly destroyed by mechanical abrasion; which 

 is not the fact, for the microscope reveals the truth, the presence of 

 the mycehum of a fungus and its destructive work on the wood fibers 

 as an important reason of their rapid abrasion. 



The chestnut is lighter than the white oak and many of the wood 

 fibers much coarser, which enables it to be impregnated with an anti- 

 septic quite readily. The large ducts of the two woods are about 

 the same size. The medullary rays of the chestnut are fewer than 

 of the white oak, and it is, therefore, more easily indented as a tie. 



The fungus which principally attacks the white cedar, Ghavioecypari^ 

 splueroidea, Spach., is Agaricu$ campaneUa, Batsch. It even attacks the 

 growing tree, and in most cases its myceliiim is fouud in the ties 

 when cut. The tree is a very slow grower and, as the lower limbs 

 become shaded, they die and are attacked by their sjiecial fungus, and 

 this communicates with the upright cells of the tree. It takes from 

 ten to twenty years before the limbs break off and the wound or orifice 

 is closed by the growing wood. As long as air has access to the 

 mycelium it slowly grows and desti'oys the wood above and below the 

 wound, the decay spreading laterally very slowly, owing to the small 

 medullary rays and the ijresei-vativcs they contain. As soon as the 

 orifice is closed, shutting off the air supply, the decay for the time 

 is nearly if not entirely checked. When the trees are cut for ties it 

 is not uncommon to find one or more decayed spDts, from one-half lo 

 an inch in diameter, extending nearly the entire length of the tie. 



The durability of the wood is so great that such ties are not 

 rejected as long as there is sufficient sound wood for spiking. This 

 wood contains a natui-al preservative and is very durable in contact 

 with the soil, but its structure is too light and delicate to long vrith- 

 stand the heavy traflic of trunk lines, though from its diu-ability it is 

 valuable for those of moderate traffic. 



The fungi which destroy ties made of Tamarack, Larix Americana, 

 Mx., are Polyporus pinicola, Fr. and Trametes Pini, Fr. 



The fruit of the former always shows traces of phosphoric acid. 



This wood is heavier than white cedar, the wood cells being larger,^ 

 with thicker walls. It is also much stronger because the cells in the; 

 annual layer formed in the autumn are neaidy soHd and in sufiicient 

 number to resist indentation or cutting of the ties by the rails under-; 



